Supporting Information: ph-triggered aggregation of responsive polymer-stabilized colloids and the reversible formation of porous scaffolds Robert T. Woodward, Christopher Hight, Ufuk Yildiz, Nicolas Schaeffer, Esther M. Valliant, Julian R. Jones, Molly M. Stevens, Jonathan V. M. Weaver* Materials. Methacrylic acid (MA), ethyleneglycol dimethacrylate (EGDMA), poly(ethylene glycol) methacrylate (PEGMA, M n = 1,100 g.mol -1 ), 1-dodecanethiol (DDT), Toluidine Blue O, ethanol, poly(methyl methacrylate) (PMMA, M w = 15,000 g.mol -1 ) and Nile Red were purchased from Aldrich and used as received. Polymer Characterization. Triple-detection GPC was performed in THF eluent on branched copolymer samples following esterification of the carboxylic acid residues of the PMA using TMS-diazomethane as described previously (R. T. Woodward, J. V. M. Weaver, Polym. Chem., 2011, 2, 403). Colloid size determination. Colloid sizes and size distributions were measured by dynamic light scattering (DLS) and laser diffraction. The inherent limitation in the sizing of particles by DLS (i.e., restricted to sub-micron) meant that the colloids could only be accurately sized by DLS in their dispersed state (i.e., basic ph). The broader sizing regime for laser diffraction meant that this technique was employed to study the (reversible) assembly of the colloids into higher-order aggregates. The two different techniques produced slightly different measured colloid diameters, but these were in reasonable agreement considering the polydispersities of the samples. The general measurement process was as follows: 3 ml of the dilute colloid solution was added to the dispersion unit containing 60 ml water (ph adjusted to ph 10 using 1 M NaOH) with a stirring rate of 1000 rpm. The volume-average diameters (D4/3) quoted are obtained from at least 5 repeat runs (D4/3 = Di4Ni/ Di3Ni). The span is a measure of the distribution of the particle size distribution and is expressed mathematically as (D(0.9) D(0.1))/D(0.5), where D(0.9) is the diameter under which 90 % of the particles fall, D(0.5) is the diameter under which 50 % of the particles fall and D(0.1) is the diameter under which 10 % of the particles fall. DLS measurements were carried out using a Malvern Zetasizer (Nano series) Nano-ZS equipped with a 633 nm laser. The scattering angle used was 175 o and all samples were measured in a disposable polystyrene cuvette. Colloid imaging. Confocal images of the particles were obtained using confocal microscopy (Zeiss LSM710 microscope with a Fluar 40x/ 1.30 Oil M27 NA Objective with excitation in the range of 515-530 and emission of Nile Red detected between 525 and 605 nm). An identical particle preparation technique was followed however Nile Red (0.05 w/v %) was dissolved in the oil phase prior to homogenization. Upon removal of the ethyl acetate, PMMA/Nile Red
particles were prepared, these were then imaged at both ph 10 and ph 2 (ph was adjusted using 1M NaOH and 1M HCl respectively). Images of emulsion droplets were obtained using light microscopy (calibrated Meiji MX9300 microscope equipped with digital camera) using a 40x magnification lens. Emulsions were prepared and measured immediately, in order to obtain images of the resulting droplet templates before the removal of the volatile ethyl acetate oil phase. Scanning electron microscopy samples were mounted on carbon tabs and coated with carbon and copper (~5 nm thickness) prior to imaging to avoid charge build up. Imaging was carried out on a Gemini 1525 FEGSEM with an acceleration voltage of 5kV. Measuring aggregation of colloids: Colloidal aggregation was measured using the same laser diffraction protocol described above. After three measurements of the colloids at ph 10 (dispersed state), the ph was lowered by addition of HCl (0.8 ml, 1 M), and the average size was measured every minute. After 7 measurements at ph 2, the ph was returned to around ph 10 via the addition of NaOH (1 ml, 1 M). The repeated reversible aggregation/redispersion measurements were performed by cycling the solution ph repeatedly using repeated HCl and NaOH additions and checking the solution ph after each addition. Quantification of residual, un-adsorbed branched copolymer by ICP. The sulphur content of the supernatants after successive washings were quantified by inductively coupled plasma optical emission spectroscopy (ICP-OES icap 6000, ThermoScientific). A calibration line was produced using solutions of known concentrations of the same sulphur-containing branched copolymer standard (0, 1, 5 and 20 ppm). Sample concentrations were calculated using the linear plot of the calibration line see Figure S3. Qualitative adsorption of cationic dye to colloid surfaces. Aqueous solutions of PMMA colloids with three different branched copolymer stabilizers (EG:MA 1:0, EG:MA 1:1 and EG:MA 2:1) were prepared at ph 10. Each solution was mixed with an aqueous solution of Toluidine Blue O (0.5 mm) at ph 10 for 1h. The colloid/dye dispersions were then centrifuged (14,000 rpm, 20 mins) to isolate the colloids along with any surface-adsorbed dye. The water phase was replaced with fresh water (ph 10) and the particles redispersed by stirring overnight. The resulting dispersions were then centrifuged once more to separate from any desorbed dye, dried and digital images were recorded to qualitatively show the levels of dye adsorbed on the colloid surfaces.
Gravimetric weight loss during monolith dehydration. Thermogravimetric analyses were performed using a Q5000IR analyzer (TA Instruments) with an automated vertical overhead thermobalance. The pellets were placed in the instrument pan immediately after formation and held at 25 C (298.15 K) under an air atmosphere for 24 hrs with measurements recorded at 10 minute intervals. Nitrogen sorption measurements. Nitrogen sorption measurements were carried out using a Quantachrome Autosorb 6B, Model AS6 KR. Samples were degassed >16 h at room temperature with a Quantachrome Autosorb degasser Model AD4. The Brunauer-Emmett- Teller (BET) method was used to determine the surface area by applying a linear correlation to eleven data points. 1 Mercury intrusion porosimetry measurements. Intrusion volumes and macropore size distributions were recorded using a Micromeritics Autopore IV 9500 porosimeter. Figure S1. Light micrograph of ethyl acetate/pmma-in water droplets at ph 10 immediately after homogenization.
Figure S2. Overlayed colloid size distribution plots of the EG:MA 1:1 (Blue data) and EG:MA 2:1 (Red data) branched copolymer stabilized PMMA colloids at ph 10 determined by DLS. Figure S3. Inductively Coupled Plasma spectroscopy data for the calculation of the level of un-adsorbed branched copolymer following colloid formation and washings. The three data points are repeat experiments to measure the concentration of unadsorbed branched copolymer surfactant after 2 washes. The average of these 3 measurements is 0.028% which corresponds to a % unadsorbed polymer of 1.4%.
Figure S4. Qualitative measurement of colloid surface charge via electrostatic adsorption of cationic dye to colloid surfaces comprising: (a) 0 % PMA residues, (b) 50 % PMA residues and (c) 66 % PMA residues. (% residues reflect ratio of PMA to ethyleneglycol repeat units) 1 IUPAC, Pure and Applied Chemistry, 1985, 57, 603-619.